The present invention relates to a display device equipped with a double sided panel in which display panels such as passive matrix liquid crystal panels, active matrix liquid crystal panels, and organic EL panels are disposed on both sides of the display device. The present invention also relates to an electronic device such as a cellular telephone that uses the display device.
In a conventional display device, for example, an STN liquid crystal display device, segmented electrodes and common electrodes are arranged in a matrix shape, forming a dot matrix. An orientation film of polyimide or the like is formed on a surface of each of the electrodes, and a liquid crystal layer is provided between the electrode surface and the orientation film. A screen is driven by applying voltage to each of the electrodes in a time division manner. Segmented signals and common signals differ from each other. An output electrode of a driver IC is connected to each of the electrodes that configure the dot matrix, and the driver IC applies signals. One chip is used to configure the driver IC that outputs the segmented signals and the common signals when the number of pixels is on the order of 160×128 dots. When the number of pixels is greater than 160×128 dots, however, specialized drivers are used as the driver IC for the segmented signals and the common signals. A plurality of driver ICs may also be used depending upon the relationship between the number of output driver signals from the driver ICs and the number of pixels.
Clamshell type structures that open into two parts have been widely employed in cellular telephones in recent years. Particular structures in which a main screen and a rear surface sub-screen are installed as display screens so that the two screens perform display on both sides of the cellular phone (hereinafter called a double sided panel) have been increasing. The two screens are configured by using separate display panels (refer to JP 2000-338483 A, for example). Separate ICs for driving the display panels are respectively mounted to the display panels to drive both of the screens. Alternatively, there is also a method of driving the two screens by using one driver IC corresponding to the combined number of pixels of both display screens. When the STN liquid crystal display devices are used in this method, for example, the segmented signals are drawn out from a side that is opposite to a side connected to the main display panel. The main display panel is connected to the sub-display panel by a film substrate to share the segmented signals. Further, the common electrodes are disposed on both sides of connection terminals for the segmented signals. Dedicated signals used only for the sub-screen are connected to the main display panel on both sides of the common electrodes used by the main display panel. The dedicated signals used for the sub-screen are connected to the sub-display panel via an outer circumference of the main display panel, similar to the segmented signals, and thus drive both screens. Alternatively, with a method of branching off the signals output from the ICs at the terminals connected to the main display panel by, for example, connecting to the sub-display panel using a flexible substrate, the common signals can also be shared, not only the segmented signals.
Problems, however, exist with the double-sided panel driven by one chip sharing signals. That is the same signals are applied to the sub-display panel as those applied to the main display panel, and thus, the main display panel and the sub-display panel turn on at the same time. Other persons can therefore see the image displayed on the sub-display panel when the cellular telephone is being operated from the main display panel, and security is not maintained.